1. Field of the Invention
The present invention relates to a DC motor, and in particular, to a brushless DC motor control apparatus and control method thereof.
2. Description of the Related Art
The motor is a kind of energy conversion device, which converts electric energy to rotational or linear kinetic energy by means of electromagnetic phenomena. With the expansion of its fields of application due to the widespread use of electronic equipment in the electric, electronic, and mechanical industries, the importance of the motor is increasing as a critical source of driving power. In addition, with the rapid growth of the industries, motors as driving sources are being created with faster speeds and greater capacities.
In particular, precision control motors provide precision movement with fast response times and wide ranges in speed control. These motors are operated according to control signals by repeating stop, start, and reverse actions, etc. Precision control motors are continually increasing in importance with the advance of technology and expansion of application fields such as advances in power electronics, advances in microcomputers, practical application of precision technology and high performance permanent magnets, and advances in surface mounting technology.
Examples of precision control motors include stepping motors and brushless DC motors, which usually use high performance permanent magnets.
The motor used most often for positioning control is the stepping motor. In the precision control of mechanical displacement in general, stepping motors are suitable for use in micoms because they allow digitalized control by using pulses. Stepping motors can provide rotation of a specified angle and can stop with a high level of precision without feedback for detecting the position of the motor shaft. Also, stepping motors can allow open loop control, provide easy control with digital signals, and have a maintenance torque when stopping.
However, the torque is low in these motors, so that they are difficult to apply in fields requiring high torque. Also, vibration and resonance phenomena are likely to appear at certain frequencies, they are weak against loads with inertia, and stepping out occurs during high-speed operations. Further, since a sufficient current cannot flow through the wound coils due to the inductance effect of the wound coils during operation with a common driver, the torque is reduced with increasing pulse rate to yield a lower efficiency as compared to a DC motor.
Thus, the brushless DC motor, which provides high torque, is preferred in controlling the position or the number of revolutions. Not only is the brushless DC motor durable and efficient, it allows for easy use in constant speed and variable speed control.
The brushless DC motor is devised without the brush, which acts as a commutator, while maintaining the properties of a DC motor, and can be classified as a sensor type or a sensorless type according to whether or not it has a sensor which detects both the position of the rotor and the rotation speed.
In a published Korean patent application no. 1998-0013970, a “positioning control method of a sensorless BLDC motor” is disclosed. It relates to a BLDC motor, wherein the counter electromotive forces generated on the stator by the rotor of the motor are detected, and pulses are divided into a multiple number, as these counter electromotive forces are compared with a standard voltage. The pulses are counted to determine the accurate position of the rotor of the motor with regard to the normal position of the rotor in the motor, and corresponding control signals are outputted to provide accurate positioning control.
This positioning control based on the control signals are for controlling the rotational position of the rotor of the motor, and cannot control the number of revolutions of the rotor.